The Online Publishers Association (OPA) released a white paper Thursday that seeks to define dayparts in an effort to give publishers better metrics to prove the Internet's strength as a marketing vehicle.

The study, done with data collected by Nielsen//NetRatings in September 2002, concludes that the five dayparts exist for Internet use: early morning (6 a.m. to 8 a.m.), daytime (8 a.m. to 5 p.m.), evening (5 p.m. to 11 p.m.), late night (11 p.m. to 6 a.m.), and weekends.

"This showed there were some unique online dayparts we could identify," said Michael Zimbalist, the OPA's executive director. "We also wanted to find how usage changed by daypart."

Not surprisingly, the study echoed the OPA's long contention that the Internet content sites are the best place to reach people during the daytime, drawing 3.8 million users per minute. This stands in contrast to Internet utilities like search, chat and e-mail, which are used evenly throughout the day.

For marketers, daytime hours offer the largest daypart, in terms of audience size and usage minutes. It's also the time to reach the most affluent. The OPA found that 25-to 54-year olds, often stuck at their desks at work, represent the largest share of daytime Internet users. For this reason, news and information sites do well, traffic-wise. At night and on weekends, however, entertainment and sports sites take over, as adults unwind and children go online.

Unlike the NAA report, the OPA does not further break down the daytime hours. However, the group said it was conducting further research with Millward Brown Intelliquest to obtain a more granular picture of the daytime Internet audience. The OPA expects to release that study's findings in the second quarter.

The push to market Internet advertising in dayparts is part of publishers' effort to speak in the language understood by advertisers and agencies geared to working in traditional media. In television, the fact that the audience composition is vastly different during the day and at night is a given.

However, online advertisers have been slow to embrace the concept online. Zimbalist said an informal poll of OPA members, which include the online units of most newspapers, found that many offered some kind of daypart option, although for the most part, they haven't aggressively marketed it to advertisers.

CBS Marketwatch was a trailblazer, running Budweiser "happy hour" ads on Friday afternoons back in 2001. Last June, NYTimes.com debuted "Site Sessions," which give a sponsor prominent placement throughout the site at a set time. In October, AOL announced it would begin selling time-targeted ads. Yahoo! has sold dayparts since 2001, and its ad chief solutions officer, Tim Sanders, sang the praises of dayparts at last year's @d:Tech conference.

"If you compare where this is today to where it was a year ago, I think it takes a long time for data to disseminate through the market," Zimbalist said. "The amount of dayparting now is much greater than a year ago."

Zimbalist said key advertising sectors, such as entertainment and food, have begun experimenting in running daypart ads. He pointed out online movie ads increasingly appear on Thursday and Friday afternoons, when research shows most people begin to make weekend entertainment decisions.

Dayparts are attractive to publishers mostly because they can charge a sizable premium during work hours, when Internet advertisers are five times more likely than television advertisers to reach consumers, according to the NAA study. Officials at NYTimes.com have said daypart-targeted ads can retrieve a 25 percent premium.